Sealants are typically synthetic resins that are soft enough to pour or extrude and readily harden or solidify to form a permanent bond with the substrate on which it is coated. They are generally used to exclude dust, dirt, moisture, gases, and chemicals. They can also be used to reduce noise and vibrations, and even to insulate. As used herein, caulks are included within the meaning of the term sealant.
One type of commercially available sealant is made of polysulfide polymers. See, for example, U.S. Pat. No. 3,297,473 (Bulbenko, issued Jan. 10, 1967) and U.S. Pat. No. 3,317,461 (Pleuddemann, issued May 2, 1967). Typically, the polysulfide polymers in sealants are thiol-terminated liquids that are convertible to the solid state. Such liquid polysulfides are available under the trade name LP by Morton Thiokol Corporation.
Polysulfide sealants do not effectively adhere to inorganic or organic surfaces. For example, under conditions of high moisture they do not adhere effectively to inorganic surfaces, such as glass, ceramic, concrete, or metal surfaces. Thus, adhesion promoters are typically used to enhance the strength of the adherence or bonding of the sealant to the surface. For example, phenolic-based adhesion promoters are used to enhance adhesion of polysulfide sealants to metals, whereas silane-based adhesion promoters are used to enhance adhesion to glass. There is need, however, for an adhesion promoter to enhance adhesion of polysulfide sealants to organic polymers such as nylon, polypropylene, and polyvinyl chloride, for example.
The petroleum and construction industries coat steel with nylon to inhibit corrosion of the steel. Furthermore, structural components, such as wood or steel beams, will be replaced more by polypropylene or nylon beams. The automotive industry use polypropylene and/or nylon to coat parts, such as bumpers, or to replace steel gas tanks, for example, as a weight saving advantage. The current polysulfide sealants actually contain phenolic-based adhesion promoters; however, these do not adhere well to such substrates. That is, the adhesion and cohesion such sealants exhibit are not generally acceptable to the end user for adhesion to nylon and polypropylene.
Silane coupling agents, such as those produced by Union Carbide under the trade designations A-189, Y-9194, and A-1120, and monoalkoxy titanate coupling agents, such as that produced by Kenrich (Bayonne, N.J.) under the trade designation KRTTS, have been suggested to enhance polysulfide sealant adhesion to glass, metal, and even plastics. Unfortunately, however, these adhesion promoters do not function with 100% cohesive failure of the sealant to the substrate. That is, the bond between the sealant and the substrate fails before the sealant itself fails internally. Thus, there is need for an adhesion promoter that enhances the adhesion between polysulfide sealants and organic polymers, particularly for adhesion promoters that function with 100% cohesive failure of a polysulfide sealant to an organic polymer, such as nylon, polyvinyl chloride, and polypropylene.